Ultraviolet radiation or UV radiation is often used to photochemically polymerize or cure various types of materials on substrates and may be used in other applications. Existing technology for performing this type of polymerization usually comprises either an electrode-powered ultraviolet lamp or a microwave-powered ultraviolet lamp. The electrode or microwave power is dissipated in a plasma-filled lamp bulb. The plasma radiates light at the desired wavelength or wavelengths and the light is typically reflected or otherwise focused on the intended target to achieve the most efficient transmission.
Microwave powered lamp assemblies generally are much more powerful than electrode powered assemblies and emit much higher UV radiation from the plasma-filled bulb. Several hundred watts of microwave power may be absorbed by the plasma in a relatively small volume. Some of this microwave power is converted to heat and, therefore, the plasma-filled bulb must be cooled in some manner to prevent overheating and promote long bulb life. Typically, cooling is achieved by circulating air over the lamp bulb. Since the microwave powered lamps generate more intense UV radiation, safety is also a concern since exposure to such radiation may raise health concerns. Finally, while microwave powered lampheads are faster to cycle on and off than electrode powered lampheads, they may still not cycle on and off quickly enough to achieve a desired production speed. In this regard, some photopolymers may have short activation periods and, therefore, it would be desirable to cycle the bulb on and off within a short period of time, for example, of several seconds or less. In a high production environment, it may also be desirable to reactivate the lamp bulb for the next curing operation on an assembly line, for example, within a very short period of time. Unfortunately, even microwave powered lampheads take time to reach full power after they have been deactivated or turned off. This time period to power up the lamp may take several seconds or more and this may be unacceptable for certain production environments.
To alleviate the problems mentioned above, as well other problems in the art, it would be desirable to provide a microwave powered lamphead which is capable of quickly cycling between active and inactive states, yet also allows proper cooling of the lamp bulb and minimizes the escape of harmful UV radiation.